Fat-Free Mass Index Controlled for Age and Sex and Malnutrition Are Predictors of Survival in Interstitial Lung Disease

Background: Literature focusing on nutritional variables and survival in interstitial lung disease (ILD) is limited by its focus on weight and BMI and has not considered body composition. Objectives: The primary objective of this study was to examine whether body composition measures, specifically fat-free mass index z-score (z-FFMI) and body fat mass index z-score (z-BFMI), were predictors of survival in fibrotic ILD patients. The second objective was to examine if nutrition status was a predictor of survival. Method: Seventy-eight outpatients diagnosed with fibrotic ILD were recruited in this cross-sectional study. Body composition data using dual frequency bioelectrical impedance analysis (BodyStat 1500MD; UK) and nutrition status using the subjective global assessment (SGA) were determined. To control for age and sex, z-FFMI and z-BFMI were calculated using population means. Participant charts were reviewed for diagnosis, age, disease severity, and exercise capacity. Results: Age (HR 1.08, 95% CI [1.03-1.13], p < 0.01), BMI (HR 0.90, 95% CI [0.84-0.97], p < 0.01]), z-FFMI (HR 0.70, 95% CI [0.56-0.87], p = 0.02), z-BFMI (HR 0.74, 95% CI [0.57-0.96], p < 0.01), 6-min walk distance (6MWD) (HR 0.99, 95% CI [0.99-1.00], p < 0.01), percent predicted diffusing capacity for carbon monoxide (%DLco) (HR 0.93, 95% CI [0.89-0.97], p < 0.01), and severe malnutrition (SGA-C) (HR 6.98, 95% CI [2.00-24.27], p < 0.01) were significant predictors of survival. When controlled for exercise capacity and disease severity, z-FFMI and severe malnutrition were significant predictors of survival independent of %DLco. Conclusion: z-FFMI and severe malnutrition were significant predictors of survival in fibrotic ILD patients independent of disease severity.